This application claims the priority of Korean Patent Application No. 2003-38517, filed on Jun. 14, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a display device, and more particularly to a display device shared between a digital-to-analog converter for outputting a convergence signal and a digital-to-analog converter for outputting a dynamic focus signal, in a projection television using 3 cathode-ray tube projection optics.
2. Description of the Related Art
A projection television includes cathode ray tubes (CRTs) which display red (R), green (G), and blue (B) color images and projects the R, G, and B color images on a screen, respectively.
As shown in FIG. 1A, R, G, and B color images R 100a, G 101a, and B 102a are projected in a biased state on a screen. Thus, a convergence correction is quite important to adjust the display of the R, G, and B color images 100a, 101a, and 102a on the screen so that an image 103a is formed.
FIG. 1B is a block diagram of a conventional convergence correction device. Referring to FIG. 1B, a convergence corrector and operation processor 100b adjusts a convergence using input horizontal and vertical sync signals. The convergence corrector and operation processor 100b performs convergence correction and operation to adjust R and B images to a G image.
The convergence corrector and operation processor 100b outputs corrected horizontal and vertical R, G, and B signals. A digital-to-analog converter (DAC) 101b, having first through sixth DACs, converts the corrected horizontal and vertical R, G, and B signals into analog convergence correction signals, respectively.
A low pass filter (LPF) 102b, having first through sixth LPFs, low-pass filters the analog convergence correction signals, respectively.
An amplifier 103b, having first through sixth amplifiers, amplifies the analog convergence correction signals, respectively. The amplified analog convergence correction signals are output to a screen (not shown).
As shown in FIG. 1C, in the projection television, R, G, and B CRTs 100c, 101c, and 102c project R, G, and B image signals, respectively. Lenses 103c, 104c, and 105c magnify the R, G, and B image signals, respectively. The magnified R, G, and B image signals are projected and displayed as one image on a screen 106c. However, the image is not clear due to different focuses on the central and peripheral portions of the screen 106c. A focus controller is needed to correct this.
FIG. 1D is a block diagram of a conventional dynamic focus controller. Referring to FIG. 1D, a dynamic focus operation processor 100d performs a dynamic focus control using input horizontal and vertical sync signals. The dynamic focus operation processor 100d performs an operation to transmit peripheral CRT beams to a screen (not shown) faster than a central CRT beam so as to output a dynamic focus control signal.
A DAC 101d converts the dynamic focus control signal into an analog dynamic focus control signal.
An LPF 102d low-pass filters the analog dynamic focus control signal.
An AMP 103d amplifies the analog dynamic focus control signal and outputs a final dynamic focus control signal, i.e., a parabolic wave.
FIG. 2A is a block diagram of another example of a conventional convergence correction device. Referring to FIG. 2A, a convergence corrector and operation processor 200a adjusts a convergence using input horizontal and vertical sync signals. The convergence corrector and operation processor 200a performs convergence correction and operation to adjust R and B color images to a G color image.
The convergence corrector and operation processor 200a outputs corrected horizontal and vertical R, G, and B signals. A first DAC 201a converts the horizontal R, G, and B signals into analog R, G, and B signals.
A second DAC 202a converts the vertical R, G, and B signals into analog R, G, and B signals.
A multiplexer (MUX) 203a selects the first DAC 201a or the second DAC 202a in response to a selection control signal output from the convergence corrector and operation processor 200a to output a horizontal R signal, a vertical R signal, a horizontal G signal, a vertical G signal, a horizontal B signal, and a vertical B signal.
An LPF 204a, having first through sixth LPFs, low-pass filters the horizontal R signal, the vertical R signal, the horizontal G signal, the vertical G signal, the horizontal B signal, and the vertical B signal, respectively.
An AMP 205a, having first through sixth AMPs, amplifies the horizontal R signal, the vertical R signal, the horizontal G signal, the vertical G signal, the horizontal B signal, and the vertical B signal, respectively, and outputs them to a screen (not shown).
FIG. 2B is a block diagram of another example of a conventional dynamic focus controller. The conventional dynamic focus controller of FIG. 2B is the same as that of FIG. 1D and thus will not be described herein.
U.S. Pat. No. 5,614,792 discloses such convergence correction and dynamic focus control.
As described with reference to FIGS. 1A through 1D, 2A, and 2B, the conventional convergence correction device and dynamic focus controller are separately installed and operated in the projection television. Thus, a plurality of DACs are needed to convert convergence correction signals and a dynamic focus control signal into analog convergence correction signals and an analog dynamic focus control signal. Accordingly, since a large number of components are necessary, the configuration of hardware is complicated, which increases the material cost.